Electron tube



Dec. 29, 1964 H. BENDER ETAL 3,163,795

ELECTRON TUBE Original Filed March 14, 1957 IN V EN TOR.

HARRY BENDER BY HARRY. P KUNG I ATTORNEY ire Stats 2 (Zlainrs. (Cl.SIB-27d) Our invention is directed toward electron discharge devices andmore particularly relates to cathodes for use therein. This applicationis a division of application Serial No. 646,010, filed March 14, 1957,now abandoned.

As is Well known to the art, the cathode or electron emissive element ofa cathode is conventionally composed of nickel or a nickel-rich alloy.In forming the element which is normally either planar or cylindrical inshape, the nickel or a mixture of nickel and certain well knownadditives, as for example magnesium or tungsten, are first melted,either in air or in vacuo, to form a billet. The billet is subsequentlyrolled and annealed to form a sheet from which the cathode elements aresubsequently fabricated.

The composition of the cathode must be controlled within extremely closetolerances to prevent impairment of electrical and structuralproperties. Such control is extremely difficult, both because of thesetolerances and further because extensive testing of the final product isnecessary to determine whether or not the final product meets thenecessary specifications. The rejection rate is extremely high, and acostly process results.

In our attempt to decrease the cathode rejection rate and thus todecrease the costs of producing cathodes, we discovered that, whenpowder metallurgy techniques were used in the manufacture of cathodes, amuch higher degree of composition control was obtained and thus therejection rate was sharply decreased.

Surprisingly, however, we also discovered that the cathodes so producedexhibited certain previously unsuspected but highly desirableproperties. In particular, We found that the strength'of these cathodessubstantially exceeded that of conventional indirectly heated cathodes,a highly significant improvement in a field where ever increasingemphasis has been placed on the development of stronger cathodes for usein electron discharge devices which are subject to severe vibrations andother types of mechanical stress.

We further discovered that when our cathodes were fabricated intoelectron tubes and tested, the sublima tion of certain additives, suchas magnesium, was sharply reduced over that conventionally obtainable,thus minimizing leakage and other factors adversely aifected by suchsublimation.

It is, therefore, an object of our invention to increase the strength ofcathodes.

Another object is to reduce the costs of manufacturing cathodes throughuse of powder metallurgy techniques.

Still another object is to provide a new process for producing cathodes.

Yet another object is to provide new and improved cathodes, the strengthof which substantially exceeds that of conventional cathodes.

Still a further object is to reduce sublimation of metals, such asmagnesium, during testing and operation of electron tubes.

sheet which is then reduced to desired dimensions in ac-v cordance withconventional rolling and annealing schedules and then fabricated, forexample, into planar or cylindrical cathodes.

The composition of cathodes so formed can .be so accurately controlledthat the compositions of successive batches (within the limits ofexperimental errors of analysis) have been found to be identical.Moreover, the strength of such cathodes is greatly increased overnormal, the collapse strength being on the order of 2 to 3 times aslarge as that of conventional cathodes. Further, the sublimation rate ofour cathodes when inserted into tubes and tested, is reduced by a factorof ten or more as compared to that conventionally obtained.

We found that the oxygen content of our cathodes is substantially inexcess of the oxygen content of conventional cathodes, the ratio of theoxygen content of our cathode to that of conventional cathodes havingotherwise substantially identical composition ranging from a minimum ofabout 2 to a maximum of 10 or more.

While it is not our intention to be bound by theory, We believe thatthis increased oxygen content plays a primary role in the increasedstrength of our cathodes. More particularly, it is our belief that theoxide which is normally formed about the surface of metal powders is notreduced during rolling and sintering, but rather remains as discreteoxide particles within the sintered sheet. Such particles apparentlyinhibit grain movement and deformation, thus stiffening andstrengthening the sheet structure.

Our invention will now be described in more detail with reference to theaccompanying figure which shows an electron tube incorporating one ofour cathodes.

Referring now to the figure, an evacuated tube envelope 10 is secured toa tube base 12. An indirectly heated cathode containing one of ourcathodes in the form of a sleeve or cylinder 18 coated with an electronemissive coating 19 and a folded heater 14 is positioned within theenvelope. A grid wire 20 and an anode 22 are also supported within theenvelope by mica spacers 2 4 and 26 which, in turn, are supported onwire supports 38 and 32.

This cathode is fabricated by first thoroughly blending nickel powder ofhigh purity either without additions or with powder additives in theform of metal or intermetallic alloys. The blended powders are thenpassed through a rolling mill to form a fragile porous sheet. The sheetis then sintered in an oxygen free atmosphere, such as argon or dryhydrogen, at a temperature falling within the approximate range 800C.1150 C. until the porosity is greatly reduced and a strong relativelynonwithin the limits of experimental errors of analysis are identical incomposition,

Example I A cathode sleeve was prepared having the followingcomposition:

the remainder being nickel with small amounts of nitrogen, hydrogen andoxygen.

All trace ingredients other than magnesium were present in the highpurity nickle powder; the magnesium was added in the form of anintermetallic alloy of nickel and magnesium, the chemical formula beingNi Mg.

The above alloy was analyzed for its gas content and was found tocontain 0.001% by weight of nitrogen, 0.001% by weight of hydrogen, and0.020% by weight of oxygen. 7

A conventional nickel-magnesium cathode was analyzed and found tocontain about 0.0042% by weight of oxygen, all other composition nangesbeing substantially identical with that of our cathode.

Our cathode and the conventional or control cathode were tested forcollapse strength; the control cathode was found to have a stiffness of460 grams, while our cathode had a stiffness of 578 grams.

Tubes of the type commercially designated as 12BA6 were fabricated usingboth types of cathodes and were tested. After a complete life test, thetwo types of cathodes. were removed from the tubes and again tested forcollapse strength; the control cathode was found to have a stiffness of180 grams while our cathode was found to have a stiffness of 420 grams.

Emission measurements showed that the emission within tubes having ourcathodes was at least equal to that obtained within tubes having thecontrol cathodes.

The conductivity as measured between the cathode and the control oftubes employing our cathodes ranged between 1/10 to 1/ 100 of theconductivity of tubes employing the controlcathode. The conductivity isdirectly related to. the degree of sublimation of the metallic elementsother than nickel present within the cathode, and hence this test showsthat the sublimation in the control tube is at least times as large asthe sublimation in tubes employing our cathodes.

Further tests showed that the oxygen content of our 4 sleeve could bedecreased to about 0.010% by weight or could be increased to about0.100% by weight without deleterious eifect. Reductions in oxygencontent below 0.010% by weight resulted in decreased stiffness, whileincreasing the oxygen content above about 0.100% caused the sleeve tobecome somewhat brittle although the stillness was not adverselyeffected.

While the sublimation of our cathodes when incorporated in a tube wasalways less than conventionally obtainable, we found that bestsublimation results were obtained by maintaining the magnesium contentwithin the range 0.05% to 0.12% by weight.

Both types of cathodes, i.e. our cathodes and control cathodes, werefabricated from pure nickel and tested in the manner indicated. It wasfound that the emission of both cathodes decreased in the sameproportion, the stiffness of both types of cathodes having about thesame values as previously indicated.

While we have shown and pointed out our invention as applied above, itwill be apparent to those skilled in the art that many modifications canbe made within the scope and sphere of our invention as defined in theclaims which follow:

What is claimed is:

l. A cathode provided with a nickel substrate and an electron emissivelayer in intimate contact with said substrate, said substrate having anoxygen content as expressed in percent by weight of said substrate whichranges between a minimum of about 0.01% and a maximum on the order of0.1%.

2. An electron discharge device having a cathode characterized by a highcollapse strength and low sublimation, said cathode being provided witha nickel substrate and an electron emissive layer in intimate contactwith said substrate, said substrate having an oxygen content whichranges between a minimum of about 0.01% by weight of said substrate anda maximum on the order of 0.1% by weight of said substrate.

References Cited by the Examiner UNITED STATES PATENTS 1,699,639 1/29Van Gessel 313346 X 2,543,439 2/51 Coomes 313-346 X 2,566,115 8/51Bounds 313346 X 2,657,325 10/53 Homer 313346 2,746,741 5/56 Naeser -2082,814,564 11/57 Hayden 75-214 FOREIGN PATENTS 700,606 12/53 GreatBritain.

DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON, ARTHUR GAUSS, Examiners.

1. A CATHODE PROVIDED WITH A NICKEL SUBSTRATE AND AN ELECTRON EMMISSIVELAYER ININTIMATE CONTACT WITH SAID SUBSTRATE, SAID SUBSTRATE HAVING ANOXYGEN CONTENT AS EXPRESSED IN PERCENT BY WEIGHT OF SAID SUBSTRATE WHICHRANGES BETWEEN A MINIMUM OF ABOUT 0.01% AND A MAXIMUM ON THE ORDER OF0.1%.